This invention relates to tape measures of the kind having a case in which is accommodated a coilable blade, i.e. measuring tape, which can be drawn out for use, a rotary carrier such as a drum discs or a spool for coiling the tape upon, and a return spring to turn the carrier so as to retract the blade into the case. More specifically, the invention is concerned with such tapes where the return spring is powerful enough to retract the blade (which is normally a flexible metal strip) without manual assistance.
It is a long standing problem that such springs can retract the tape excessively fast and cause damage. The blade may whip about as it is being retracted, buckling itself and/or striking something. Damage may be caused when the motion of the blade is abruptly halted by the end hook striking the mouthpiece of the case. In extreme instances the end hook can be torn off. Excessively fast retraction is encouraged by a requirement that the spring be powerful enough to retract a blade which is not extending straight. It also tends to arise because a manufacturer will generally make a range of tape measures; the frictional drag on retraction will vary between one model in this range and another, and the manufacturer will wish to use a return spring capable of overcoming the greatest friction encountered.
There have been proposals to overcome or alleviate this problem. One is some kind of governor arrangement depending on bob weights which are centrifuged outwardly. This serves the purpose of retarding retraction, and indeed is apt to be too effective, so that retraction of the tape seems slow. However, it requires a complex and therefore expensive assembly of parts.
One manufacturer provides a rubber "bump stop" at the mouthpiece of the case. Another uses a rubber piece threaded onto the blade so that it comes between the end hook and the mouthpiece to lessen the impact. These techniques are of course alleviating the effects rather than dealing with the cause of them.